A multi-speed bicycle is equipped with a drivetrain as shown in FIG. 1. Referring to FIG. 1, which is a schematic top view of a drivetrain 100 of a conventional multi-speed bicycle. The drivetrain 100 in FIG. 1 belongs to a 1X transmission system and includes a drive chain 110, a freewheel 120 and a chainwheel 130. The chainwheel 130 is a single chainring and is connected with a crank (not shown). The freewheel 120 has a plurality of sprockets 121 stacked on each other and is connected to a rearwheel (not shown).
The sprockets 121 and the rearwheel are co-axial, and the sizes of the sprockets 121 are different from each other. As seen in FIG. 1, the sprockets 121 are arranged from top to bottom in an order from large to small, so the uppermost sprocket 121 in FIG. 1 has the largest diameter, whereas the lowermost sprocket 121 in FIG. 1 has the smallest diameter. The drive chain 110 engages with the freewheel 120 and the chainwheel 130. When the rider presses the pedal to rotate the crank, the chainwheel 130 is driven by the crank to rotate around the rotation axis A13. At this time, the rotating chainwheel 130 drives the drive chain 110 so that the drive chain 110 transmits power to the freewheel 120. Thus, the freewheel 120 can rotate around the rotation axis A12 to rotate the rearwheel, thereby moving the multi-speed bicycle.
The drive chain 110 can selectively engage with one of the sprockets 121 to achieve a multi-speed function. In order to engage with any of the sprockets 121 of the freewheel 120, the drive chain 110 needs flexibility, that is, the magnitude of bending of the drive chain 110 along the rotation axes A12 and A13. The greater the flexibility is, the greater the magnitude of the drive chain 110 bends in the direction of the rotation axes A12 and A13 is, so that the drive chain 110 can engage with any one of the sprockets 121. However, the free section (the portion of the drive chain 110 shown by oblique virtual lines in FIG. 1) where the drive chain 110 does not engage with the freewheel 120 and the chainwheel 130 is not suitable for greater flexibility. When the drive chain 110 in the free section has greater flexibility, the drive chain 110 in the free section is easy to offset in the direction along the rotation axes A12 and A13, thereby increasing the risk of disengagement of the drive chains 110 with the freewheel 120 and the chainwheel 130.
The section of BACKGROUND OF THE INVENTION is used merely to aid in the understanding of the present disclosure, and what is disclosed in BACKGROUND OF THE INVENTION may include some of the conventional techniques that are not known to those of ordinary skill in the art. Moreover, what is disclosed in BACKGROUND OF THE INVENTION does not imply that the content or the problem to be solved by one or more embodiments of the invention and does not mean that it has been known to those of ordinary skill in the art before the application of the present disclosure.